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  • nitrogen  (47)
  • Zea mays  (28)
  • Electron microscopy
  • oxidation
  • Springer  (101)
  • PANGAEA
  • 1995-1999  (101)
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  • 1
    ISSN: 1572-9680
    Keywords: A,nus rubra ; hedgerow intercropping ; Robina pseudoacacia ; Zea mays
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The objective of this study was to determine crop and tree productivity in several alley cropping planting patterns. The four- year study was conducted in western Oregon, United States and involved irrigated sweet corn (Zea mays) intercropped between hedgerows of red alder (Alnus rubra) and black locust (Robina pseudoacacia). Three alley cropping planting patterns with variable plant populations and tree-crop proximity were tested with each tree species in a randomized block design. Space available to trees and crops determined yield of both plant components. High crop yield coincided with low pruning yield, and vice versa. Compared to monocropping, yield reductions in traditional alley cropping planting patterns with widely spaced, double tree rows ranged from 5% to 15%. A. rubra and R. pseudoacacia coppiced readily and produced 0.9 to 4.7 tons of dry matter pruning biomass per growing season, depending on planting pattern and year. A. rubra yield continually increased during the trial, while the ability of R. pseudoacacia to produce green manure after frequent coppicing appeared to weaken. After four years, soil organic matter was 4 to 7% higher in the topsoil of an alley cropping system compared to a monocropping system. However, continuous growing of sweet corn resulted in decreased soil organic matter levels in both cropping systems compared to original levels. Crop yield reductions and the need for additional management inputs constrain the implementation of alley cropping in temperate climates. Only if benefits other than minor soil fertility improvements are realized is alley cropping a feasible alternative in temperate climate regions.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-2145
    Keywords: Zea mays ; Calcium ; Cell integrity ; Cell viability ; Sperm cell
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Our previous studies showed that Brewbaker and Kwack salts, which have been widely used in pollen germination and sperm isolation, are not appropriate for the maintenance of isolated maize (Zea mays L.) sperm cells. In the present study, we have characterized the effects of each BKS component salt on the integrity of isolated sperm cells using hemacytometry. At 0.01 and 0.1 mM, there were no differences in cell number between control and any salt-treated cells except a 22% decrease with 0.1 mM MgSO4 at 48 h. At the 1 mM level, cell number decreased with time in the presence of Ca(NO3)2 and MgSO4, with loss of integrity of most cells at 48 h, while KNO3 and H3BO3 had little or no effect. Further characterization of calcium-induced reduction in cell integrity using flow cytometry showed that depletion of possible residual free calcium by addition of EGTA to the suspension medium improved cell longevity and viability. Exposure of isolated sperm cells to 1 mM calcium had no effect on cell integrity and viability in 5 h; however, only 12% of cells remained intact at 24 h. The reduction in cell integrity was hastened when cells were pretreated with the calcium ionophore A23187 prior to exposure to 1 mM calcium, with a 54% reduction in cell number at 1 h and complete cell lysis at 24 h. However, depletion of cytosolic free calcium by pretreatment of cells with the calcium ionophore followed by resuspension in the presence of EGTA resulted in rapid reduction of cell integrity as well. These results collectively suggest that maize sperm cells are sensitive to exogenous free calcium; however, a certain level of cytosolic free calcium is necessary for maintenance of integrity. Mechanisms of calcium-induced reduction in cell integrity are discussed along with possible roles of the sensitivity of sperm cells to calcium in fertilization.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Journal of thermal analysis and calorimetry 49 (1997), S. 745-753 
    ISSN: 1572-8943
    Keywords: DSC ; kerogen ; oxidation ; pyrolysis ; type determination
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The rate of pyrolysis and oxidation of 8 different samples of oil shale kerogen concentrate (KC) were investigated using DSC analysis. Recently performed thermogravimetric studies (TG and DTG) with the same samples of KC indicated that the activation energy of the pyrolysis of specific KCs increases with increasing paraffinic structure in the KC. An opposite effect, i.e. a decrease of the activation energy with an increase of paraffinic structure was determined in the case of KC oxidation. In this study, using the standard ASTM E-698 method based on the determined temperature at which the maximum heat effect could be observed (exo in the case of oxidation and endo in the case of pyrolysis), an activation energy for the pyrolysis, as well as for the oxidation process was determined and also successfully correlated with the content of paraffinic structure of KC. Thus, the higher content of paraffinic structure in KCs indicates that higher values of the activation energy could be determined either in the case of pyrolysis or oxidation followed by DSC analysis.
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Water, air & soil pollution 98 (1997), S. 389-399 
    ISSN: 1573-2932
    Keywords: fertilizer ; nitrogen ; pollution ; runoff ; stable isotopes ; sugarcane
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract In many forested wetlands of Louisiana, surface water quality is being deteriorated by nutrient input from adjacent agricultural production area. This field study assesses the input of fertilizer N, applied to sugarcane fields, to forested wetlands. The potential use of natural abundance variations in15N/14N ratios for identification and tracing surface water N sources (NH 4 + - and NO 3 − -N) was evaluated. Runoff and surface water samples were collected from sugarcane fields and bordering forested wetlands (6 stations) over a 16 month period and analyzed for NH 4 + -N, NO 3 − -N, and associated NH 4 + -δ 15N and NO 3 − -δ 15N ratios. FertilizerN draining into adjacent forested wetland was estimated to be only a small fraction of the amount applied. Concentrations of NH 4 + - and NO 3 − -N in the collected water samples were low and ranged from 0.02 to 1.79 mg L−1. Isotopic analysis revealed NH 4 + -δ 15N and NO 3 − -δ 15N means were distinctive and may have the potential to be used as tracers of N contamination. The mean NH 4 + -δ 15N value was +18.6±7.1‰ and the NO 3 − -δ 15N mean was +8.3±3.1‰. Anomalously high NO 3 − -δ 15N values (〉30‰) were attributed to denitrification.
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Theoretical and applied genetics 90 (1995), S. 1198-1203 
    ISSN: 1432-2242
    Keywords: Diplospory ; RFLP ; Bulk-segregant analysis ; Genome similarity ; Intergeneric hybrids ; Zea mays
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Polyploid plants in the genus Tripsacum, a wild relative of maize, reproduce through gametophytic apomixis of the diplosporous type, an asexual mode of reproduction through seed. Moving gene(s) responsible for the apomictic trait into crop plants would open new areas in plant breeding and agriculture. Efforts to transfer apomixis from Tripsacum into maize at CIMMYT resulted in numerou intergeneric F1 hybrids obtained from various Tripsacum species. A bulk-segregant analysis was carried out to identify molecular markers linked to diplospory in T. dactyloides. This was possible because of numerous genome similarities among related species in the Andropogoneae. On the basis of maize RFLP probes, three restriction fragments co-segregating with diplospory were identified in one maize-Tripsacum dactyloides F1 population that segregated 1∶1 for the mode of reproduction. The markers were also found to be linked in the maize RFLP map, on the distal end of the long arm of chromosome 6. These results support a simple inheritance of diplospory in Tripsacum. Manipulation of the mode of reproduction in maize-Tripsacum backcross generations, and implications for the transfer of apomixis into maize, are discussed.
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  • 6
    ISSN: 1573-515X
    Keywords: atmospheric deposition ; moss ; bog ; nitrogen ; phosphorus ; water table
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract Nitrogen additions as NH4NO3 corresponding to 0 (N0), 1 (N1), 3 (N3) and 10 (N10) g N m−2 yr−1 were made toSphagnum magellanicurn cores at two-week intervalsin situ at four sites across Europe, i.e. Lakkasuo (Finland). Männikjärve (Estonia), Moidach More (UK) and Côte de Braveix (France). The same treatments were applied in a glasshouse experiment in Neuchâtel (Switzerland) in which the water table depth was artificially maintained at 7, 17 and 37 cm below the moss surface. In the field, N assimilation in excess of values in wet deposition occurred in the absence of growth, but varied widely between sites, being absent in Lakkasuo (moss N∶P ratio 68) and greatest in Moidach More (N∶P 21). In the glasshouse, growth was reduced by lowering the water table without any apparent effect on N assimilation. Total N content of the moss in field sites increased as the mean depth of water table increased indicating growth limitation leading to increased N concentrations which could reduce the capacity for N retention. Greater contents of NH4 + in the underlying peat at 30 cm depth, both in response to NH4NO3 addition and in the unamended cores confirmed poor retention of inorganic N by the moss at Lakkasuo. Nitrate contents in the profiles at Lakkasuo, Moidach More, and Côte de Braveix were extremely low, even in the N10 treatment, but in Männikjärve, where the mean depth of water table was greatest and retention absent, appreciable amounts of NO3 − were detected in all cores. It is concluded that peatland drainage would reduce the capture of inorganic N in atmospheric deposition bySphagnum mosses.
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Agroforestry systems 42 (1998), S. 107-120 
    ISSN: 1572-9680
    Keywords: erosion ; Gliricidia sepium ; Oryza sativa ; Paspalum conjugatum ; Penisetum purpureum ; Zea mays
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Farming systems that minimize the rate of soil degradation and optimize food crop yields are needed to sustain soil productivity on sloping, acid, infertile soils in the humid tropics. Research was conducted on two Oxisols with slopes ranging from 22 to 30% to evaluate the performance of several contour hedgerow systems, with and without the addition of 60 kg N ha−1 per crop, on rice (Oryza sativa) and maize (Zea mays L.) production. Contour hedgerows were double rows of the tree legume Gliricidia sepium (G); Gliricidia and the native grass Paspalum conjugatum (GPas); Gliricidia and an exotic fodder grass Penisetum purpureum (GPen); double rows of Penisetum (Pen); and a conventional open field (C) farming system without hedgerows. Gliricidia prunings and all crop residues were applied to the soil surface in the alleys, but Penisetum was harvested. Food crop yields in all hedgerow treatments tended to be less than the Control for the first two years, presumably due to the displacement of land planted to the food crop. In the third and the fourth years, the rice and maize yields of Treatments G and GPas exceeded the Control, most consistently when N was not applied. Penisetum reduced food crop yields regardless of N application presumably due to nutrient removal in the fodder. The results indicate that Gliricidia in a contour hedgerow increases food crop yield on strongly acid Oxisols by recycling nutrients and partially supplementing the N demand by the food crops.
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Euphytica 90 (1996), S. 65-72 
    ISSN: 1573-5060
    Keywords: green maize ; general combining ability ; specific combining ability ; genotypic correlations ; environmental correlations ; Zea mays
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary In Trinidad, maize (Zea mays L.) is primarily harvested in the immature stage as green ears for human consumption. The purchase of popular imported hybrid seed has become a substantial component of the economic inputs of maize production. The objectives of this study were to investigate combining abilities and heterotic patterns among available open-pollinated varieties and to assess correlations among five important traits: time to silking, plant height, grain yield, ear size, and marketable ears per hectare. General combining ability was significant for all traits. Specific combining ability was significant for all traits except ear size. Three intervarietal crosses showed moderate levels of heterosis (10–27%), and several yielded similarly to the control hybrids, Pioneer X304 and Pioneer 3078. The cross Acid Soil Tolerant 1991 SA-3 X ICTA Farm Corn was selected as the most suitable base population for mass selection. Phenotypic and genotypic correlations among the five traits studied were all positive and significant. Populations which flowered early were shorter and yielded less than the late flowering and taller populations and population crosses included in this study.
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  • 9
    ISSN: 1573-515X
    Keywords: nitrogen ; particulate organic matter ; nutrient cycling ; grassland
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract A set of long term15N studies was initiated during the summers of 1981 and 1982 on the backslope and footslope, respectively, of a catena in the shortgrass steppe of northeastern Colorado. Microplots labeled with15N urea were sampled for15N and total N content in 1981 and 1982 and again in 1992. In November, 1982, 100% of the added N was recovered in the soil-plant system of the finer-textured footslope, compared to 39% in the coarser-textured backslope microplots. Ten years later,15N recovery of the applied N decreased at both topographic positions to 85% in the footslope and 29% in the backslope. Average losses since the time of application were 3.5 g N m−2yr−1 in the backslope and 0.8 g N m−2yr−1 in the footslope. In 1992, soil organic matter was physically fractionated into particulate (POM) and mineral associated (MAON) fractions and 21-day mineralization incubations were conducted to assess the relative amounts of15N that were in the slow, passive and active soil organic matter pools, respectively, of the two soils. Our findings confirm the assumptions that POM represents a large portion of the slow organic compartment and that the MAON represents a large fraction of the passive compartment defined in the Century model. The N located in the MAON had the lowest availability for plant uptake. Isotopic data were consistent with textural effects and with the Century model compartmentalization of soil organic N based on the residence time of the organic N.
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    Water, air & soil pollution 98 (1997), S. 389-399 
    ISSN: 1573-2932
    Keywords: fertilizer ; nitrogen ; pollution ; runoff ; stable isotopes ; sugarcane
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract In many forested wetlands of Louisiana, surface water quality is being deteriorated by nutrient input from adjacent agricultural production areas. This field study assesses the input of fertilizer N, applied to sugarcane fields, to forested wetlands. The potential use of natural abundance variations in 15N14N ratios for identification and tracing surface water N sources (NH 4 + - and NO3 --N) was evaluated. Runoff and surface water samples were collected from sugarcane fields and bordering forested wetlands (6 stations) over a 16 month period and analyzed for NH 4 + -N, NO 3 - -N, and associated NH 4 + -δ15N and NO 3 - -δ15N ratios. Fertilizer N draining into adjacent forested wetland was estimated to be only a small fraction of the amount applied. Concentrations of NH 4 + - and NO 3 - -N in the collected water samples were low and ranged from 0.02 to 1.79 mg L-1. Isotopic analysis revealed NH 4 + -δ15N and NO 3 - -δ15N means were distinctive and may have the potential to be used as tracers of N contamination. The mean NH 4 + -δ15N value was +18.6 ± 7.1‰ and the NO 3 - -δ15N mean was +8.3 ± 3.1‰. Anomalously high NO 3 - -δ15N values (〉30‰) were attributed to denitrification.
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